Audio systems are assembled from a combination of loudspeakers and electronics and are traditionally designed through a development phase that may include computer modeling or simulation followed by development and assembly of a physical reference system that has undergone various iterations to optimize maximum acoustic performance within constraints such as physical size, materials and cost. To quantify the capability of an audio system to accurately reproduce sounds that will be played through it performance characteristics such as frequency response may be measured with acoustic measurement equipment. Along with loudspeakers and amplifiers an audio system often includes analog or digital signal processing that can modify the natural reproduction capabilities of loudspeakers and may be applied to individual channels in a stereo or multi-channel system such as left and right in a stereo system, or the signal processing may be applied to individual channels directly to full range or frequency divided loudspeakers such as a front left mid-range, front left high frequency tweeter and so on. When the reference audio system is finalized the designs for all components such as loudspeakers are finalized for production and the equalization data developed either manually or through an automated tuning process such as described in US patent application 20070025559 “Audio Tuning System” and may be stored in a master record so that it may be recalled for embedding into production audio systems.
For the acoustic performance of duplicate audio systems such as in mass produced audio systems to closely conform to the acoustic performance of the reference audio system on which it is based the individual loudspeakers should ideally conform within a metric threshold in comparison with the individual loudspeakers used in the reference system to which each loudspeaker is associated. By associated we mean for example the specific type or model of loudspeaker and its installation location in the audio system. For example, a 16 cm loudspeaker where the model information includes all mechanical details of the subcomponents such as cone, spider and voice-coil and so on and their assembly processes is mounted in the front left door of a vehicle audio system. However in actuality performance of mass produced loudspeakers can deviate substantially as described in Audio Engineering Society (AES) Preprint #7530 “Loudspeaker Production Variance”. Consequently variance of individual duplicate production loudspeakers causes performance of duplicate production audio systems to vary from each other and in particular perform differently than the reference audio system. It would be preferable to minimize the physical variance of duplicate production loudspeakers but the required material and assembly process control will add complexity and cost to production loudspeakers. Alternatively sorting loudspeakers into performance categories based on minimal metrics threshold tolerances for grouping similar performance loudspeakers for installation into specific consumer loudspeaker systems as described in AES preprint #1485 “Production Testing of Loudspeakers Using Digital Techniques” adds complexity and cost that is not unpractical for high volume duplicate mass production audio systems and in particular for mass produced audio systems installed in vehicles.
Loudspeakers are traditionally described as operating within various electro-mechanical and acoustic metric thresholds. Some examples of metric thresholds include a frequency response that usually defines a performance bandwidth and deviation within the bandwidth, sensitivity relative to a distance and power input, voice-coil DC resistance, impedance, harmonic or total harmonic distortion, intermodulation distortion and parameters that describe the interaction of mechanical and electrical components. In addition to loudspeaker production variance loudspeakers are also prone to influences of environmental ambient conditions such as ambient temperature and ambient relative humidity as described in AES preprint 5507 “Ambient Temperature Influences on OEM Automotive Loudspeakers” and U.S. Pat. No. 7,092,536 to Hutt et al. In order to minimize measurement error it is important that ambient conditions be within a reasonable tolerance threshold for loudspeakers to be reliably and repeatably measured.
U.S. Pat. No. 5,581,621 to Yoshihide et al describes use of a programmable parametric equalizer to automatically adjust an audio system but provides no means for controlling the process to reliably or repeatably correlate results of one operation to another operation or to reliably repeat and correlate to a performance response target based on previously measured reference data. U.S. Pat. No. 5,361,305 by Easley et al describes a vehicle audio test system that utilizes radio transmission to test audio system operation but provides no means to make adjustments to the audio system to rectify loudspeaker production variance nor does it provide a means to reliably and repeatably reproduce test results.
Therefore there exists a need for a method to reliably and repeatably identify and rectify the influences of loudspeaker production variance on audio systems.